1. Field of the Invention
The present invention relates to an ink jet recording apparatus capable of obtaining high quality images on a recording medium. More particularly, the invention relates to an ink jet recording apparatus that records by discharging recording ink and processing liquid such as an image enhancement agent that insolubilizes or coagulate coloring material in ink.
The present invention is applicable to all the equipment and devices that uses a recording medium formed by paper, cloth, leather, unwoven textile or the like, or a recording medium formed even by metallic material. As specific equipment and devices to which the present invention is applicable, there is a printer, a copying machine, a facsimile equipment, or some other office equipment or those usable as industrial production equipment.
2. Related Background Art
Conventionally, an ink jet recording method has been utilized for a printer, a copying machine, or the like, because this method enables operates at lower running costs with a lesser amount of noises, while making it easier to produce apparatuses compactly, and also, to facilitate color handling.
However, if it is intended to obtain images on a recording medium, which is the so-called ordinary paper, by means of those recording apparatuses that utilize the ink jet recording method, the waterproof capability of images thus recorded becomes insufficient or when it is intended to form color images, compatibility is not obtainable in forming highly densified images having no feathering and those having no running created between colors. As a result, it is impossible to obtain color images having good image fastness, and-excellent quality as well.
In recent years, it has been made practicable to use the ink that contains waterproof coloring material in it as a method for enhancing the waterproof capability of recorded images. However, not only such waterproof capability is far from sufficient, but also, in principle, an ink of the kind is hardly soluble to water once it has been dried, which may often result in the nozzle clogging of a recording head. Therefore, there is apparently a disadvantage that the structure of the apparatus should become more complicated in order to prevent such nozzle clogging.
Also, a number of techniques have been disclosed conventionally for the enhancement of the fastness of recorded objects. In the specification of Japanese Patent Laid-Open Application No. 53-24486, a technique is disclosed, in which colors are laked and fixed by giving post-process to a colored object in order to promote wet fastness thereof.
In the specification of Japanese Patent Laid-Open Application No. 54-43733, a recording method is disclosed, in which the two or more components that promote the film formation capability when being in contact with each other at the room temperature or being heated by use of the ink jet recording method, thus making it possible to obtain a printed object whose film has been made strongly adhesive to the object when each of the components are in contact on a recording medium.
In the specification of Japanese Patent Laid-Open Application No. 55-150396, there is disclosed a method for providing water soluble color ink with the waterproofing agent for the formation of colors and lake after an ink jet recording has been executed.
In the specification of Japanese Patent Laid-Open Application No. 58-128862, an ink jet method is disclosed in which the position of an image to be recorded is discriminated beforehand, and then, recording ink and processing ink are overlaid for recording. A method is also disclosed in which a drawing is made in processing ink before recording ink is applied; processing ink is overlaid on a drawing written in recording ink beforehand; or recording ink is overlaid on a drawing written in processing ink beforehand, and processing ink is again overlaid to complete the drawing.
However, in these publications, no disclosure is made as to the recovery means, head structure, and tank structure, which are all characteristics of an ink jet recording apparatus for the maintenance of reliability of discharges, and also, as to the recording mode or the like which is needed for the enhancement of quality of recorded images.
On the other hand, there are fundamentally the problems inherent in the ink jet recording method as given below.
Firstly, ink adheres to the discharge opening surface of a recording head due to fine ink droplets (mist) generated other than the discharged main ink droplets when ink droplets are discharged from a recording head to a recording medium, such as a paper sheet, an OHP film, for recording, and ink droplets rebounded from the recording medium. If such ink is concentrated adhesively on the circumference of each discharge opening in a large quantity, or if paper particles or other foreign substances adhere to such concentration of ink, discharges are blocked, resulting in malfunction such as ink being discharged in the unexpected directions (twisting) or discharges of ink droplets being disabled (non-discharges).
Secondly, if ink in the nozzles of a recording head is evaporated and dried when printing is at rest, that is, if no discharges are made for a long time, to be exact, then overly viscous and fixed ink tends to clog the interior of nozzles to cause the twisted discharges or other defective discharges.
Therefore, in order to eliminate these unfavorable events, recovery means is provided for the ink jet recording method.
As means for cleaning and removing unwanted ink, paper particles and other foreign substances adhering to the discharge opening surface, which are caused by mist and rebounding ink droplets from a recording medium as described above as the first problem, it is generally adopted to arrange a structure in which the discharge opening surface is wiped off (wiping) by use of a blade formed by rubber or some other elastic material.
As means for solving the second problem described above, it is generally adopted to arrange the structure so that a recording head is capped to prevent ink from becoming overly viscous and fixed in the nozzle of the recording head at the time of non-recording, and that the ink, which becomes overly viscous and fixed to result in defective discharges and the adhesion of the foreign substances or the like and cannot be removed by means of the blade, is removed by exhausting the overly viscous ink from the nozzles by means of a suction pump connected with the cap for recovering the head for the performance of normal discharges. Further, for the operation of an on-demand type ink jet recording method, the plural discharge openings, which are arranged for one recording head, are not necessarily used at a time always. As a result, there are some nozzles that are not used for more than a certain period of time. Also, in a case where a plurality of recording heads are used such as for a color recording apparatus, there are some recording heads to which no data are transferred (the heads which are not currently engaged in recording), that is, the recording heads which are not used. If a carriage is caused to scan or come to a stop while the discharge opening surface of the head mounted on it is not capped, ink is evaporated and dried on the discharge opening surface and in the interior thereof from which no ink has been discharged for a certain period continuously. As a result, the discharge capability is lowered to cause the degradation of recorded images eventually. In order to prevent such phenomenon as this, it is generally practiced for an ink jet recording apparatus to discharge ink in a specific location per certain periodical interval irrespective of recording data, thus causing ink in the nozzles to be exhausted to the outside to refresh ink. In this way, the discharge condition is always maintained normally and appropriately. Such ink discharge operation as this is called pre-discharge.
Ink by the pre-discharge described above is discharged to the location called pre-discharge position arranged separately in the cap of a recovery unit so that ink thus discharged is not caused to fly over a recording medium or in the interior of the recording apparatus to stain it.
For an ink jet recording apparatus that discharges ink and processing liquid, there is proposed a structure in the specification of Japanese Patent Laid-Open Application No. 8-281968 Japanese Patent Application No. 7-202635 in which caps, pumps, and wiping means are provided separately for use of ink discharge and for use of processing liquid discharge as a pre-discharge structure which is arranged for the solution of the problems described above.
Particularly, with regard to the wiping structure, it is proposed to provide a structure in which the wiping directions of ink and processing liquid are made different when wiping is performed in the main scanning direction of a carriage. However, this proposal is still insufficient from the viewpoint of the compatibility between a higher reliability such as no ink coagulation, fixation, or the like occurring in the recording apparatus and the simplification of the wiping mechanism.
Along the demands more on higher image quality, an ink jet recording apparatus has more numbers of nozzle arrays for discharging deep and light ink or the like. In this case, if a structure is still such as to wipe the nozzle arrays by the provision of the corresponding numbers of blades, it automatically leads to the increased costs inevitably.